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package Compiler;
import java.util.ArrayList;
import java.util.List;
public class Parser {
private final List<Token> tokens;
private int currentToken = 0;
Parser(List<Token> tokens){
this.tokens=tokens;
}
List<Statement> parse(){
List<Statement> statements = new ArrayList<>();
try{
while (!checkEOF()){
statements.add(declaration());
}
}catch (Error e){
return null;
}
return statements;
}
//Clean up and reduce code mess
private Statement declaration(){
if (matchAndAdvance(TokenType.INT)){
matchOrError(TokenType.DEFINE, ":: Required for variable definition");
matchOrError(TokenType.IDENTIFIER,"Expected variable name.");
Token varName = getPreviousToken();
return new Statement.VariableDeclaration(varName,"int");
} else if (matchAndAdvance(TokenType.REAL)){
matchOrError(TokenType.DEFINE, ":: Required for variable definition");
matchOrError(TokenType.IDENTIFIER,"Expected variable name.");
Token varName = getPreviousToken();
return new Statement.VariableDeclaration(varName,"real");
//Could be improved significatly when verifiying length is a positive integer
} else if (matchAndAdvance(TokenType.STRING)){
matchOrError(TokenType.LEFT_PAREN, "Length of string must be defined");
matchOrError(TokenType.LEN, "Length of string must be defined");
matchOrError(TokenType.EQUALS, "Length of string must be defined");
Expression length = expression();
if(!(length instanceof Expression.Literal)){
throw error("String length must be a number");
}
if(!((Expression.Literal)length).type.equals("int")){
throw error("String length must be a integer");
}
if((int)((Expression.Literal)length).value.value<1){
throw error("String length must be greater then 0");
}
matchOrError(TokenType.RIGHT_PAREN, "Length of string must be defined");
matchOrError(TokenType.DEFINE, ":: Required for variable definition");
matchOrError(TokenType.IDENTIFIER,"Expected variable name.");
Token varName = getPreviousToken();
return new Statement.StringDeclaration(varName,length);
}
return statement();
}
private Statement statement(){
if (matchAndAdvance(TokenType.PRINT)){
return printStatement();
}else if (matchAndAdvance(TokenType.IF)){
Statement statement = ifStatement();
return statement;
}
return expressionStatement();
}
private Statement printStatement(){
matchOrError(TokenType.STAR, "Syntax, print *, item1, item2...");
List<Expression> exprList = new ArrayList<>();
while(!matchAndAdvance(TokenType.ENDPRINT)){
if(checkEOF()){
throw error("Missing close parentheses");
}
matchOrError(TokenType.COMMA, "Print items must be seperated by ,");
Expression expr = expression();
exprList.add(expr);
}
return new Statement.PrintStatement(exprList);
}
//Could be cleaned up to handle else statements better
private Statement ifStatement(){
Expression condition = expression();
if(matchOrError(TokenType.THEN, "then expected after if statement")){
List<Statement> statements = new ArrayList<>();
List<Statement> elseStatements = new ArrayList<>();
while(!matchAndAdvance(TokenType.ENDIF)&&!checkToken(TokenType.ELSE)){
if(checkEOF()){
throw error("endif missing");
}
statements.add(declaration());
}
if(matchAndAdvance(TokenType.ELSE)){
while(!matchAndAdvance(TokenType.ENDIF)){
if(checkEOF()){
throw error("endif missing");
}
elseStatements.add(declaration());
}
}
Statement ifstatement = new Statement.IfStatement(condition, statements,elseStatements);
return ifstatement;
}
return null;
}
private Statement expressionStatement(){
Expression expression = assignment();
return new Statement.ExpressionStatement(expression);
}
private Expression assignment(){
Expression variable = expression();
if (matchAndAdvance(TokenType.EQUALS)){
Expression assignedvalue = expression();
if (variable instanceof Expression.Variable){
return new Expression.AssignmentExpression(((Expression.Variable)variable).name,assignedvalue);
}
throw error("Incorrect assignment operation");
}
return variable;
}
private Expression expression(){
Expression createdExpression = equality();
return createdExpression;
}
private Expression equality(){
Expression createdExpression = comparison();
while (matchAndAdvance(TokenType.EQUALITY)){
Token op = getPreviousToken();
Expression right = comparison();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression comparison(){
Expression createdExpression = term();
while (matchAndAdvance(TokenType.GREATER)||matchAndAdvance(TokenType.LESS)){
Token op = getPreviousToken();
Expression right = term();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression term(){
Expression createdExpression = factor();
while (matchAndAdvance(TokenType.PLUS)||matchAndAdvance(TokenType.MINUS)){
Token op = getPreviousToken();
Expression right = factor();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression factor(){
Expression createdExpression = primary();
while (matchAndAdvance(TokenType.STAR)||matchAndAdvance(TokenType.SLASH)){
Token op = getPreviousToken();
Expression right = primary();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression primary(){
if (matchAndAdvance(TokenType.NUMBER)){
if(getPreviousToken().value instanceof Integer){
return new Expression.Literal(getPreviousToken(),"int");
} else if(getPreviousToken().value instanceof Double){
return new Expression.Literal(getPreviousToken(),"double");
}
}
if (matchAndAdvance(TokenType.STRING)){
return new Expression.Literal(getPreviousToken(), "string");
}
if (matchAndAdvance(TokenType.IDENTIFIER)) {
return new Expression.Variable(getPreviousToken());
}
if (matchAndAdvance(TokenType.LEFT_PAREN)){
Expression expr = expression();
if (matchAndAdvance(TokenType.RIGHT_PAREN)){
return new Expression.BracketedExpression(expr);
}
else{
throw error("Expected ')");
}
}
throw error("Expected Expression");
}
private void advanceToken(){
if (!checkEOF()) {
currentToken++;
};
}
private boolean matchAndAdvance(TokenType type){
if (checkToken(type)) {
advanceToken();
return true;
}
return false;
}
private boolean matchOrError(TokenType type,String errorMessage){
if (matchAndAdvance(type)){
return true;
}
throw error(errorMessage);
}
private boolean checkToken(TokenType type){
if (checkEOF()) return false;
return getCurrentToken().type == type;
}
private boolean checkEOF(){
return tokens.get(currentToken).type==TokenType.EOF;
}
private Token getCurrentToken(){
return tokens.get(currentToken);
}
private Token getPreviousToken(){
return tokens.get(currentToken - 1);
}
private Error error(String message){
Language.displayError(message);
return new Error();
}
}
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